Radio communication is widely used for conveying data between electronic devices. Typically, communicating data between electronic devices includes transmission of “packets” of digital data. Examples of devices that communicate via radio for communicating data include surveying applications, precision farming applications, etc.
In recent years, the number of persons using licensed and unlicensed frequency bands for voice communications has increased dramatically, making these frequency bands crowded, congested and unavailable for use by users that transmit digital data. Also, persons using licensed and unlicensed frequency bands for voice communications tend to communicate during business hours and during certain times of the day. At these times, desirable frequency bands become highly congested, particularly in densely populated areas, making usage for transmission of digital data difficult if not impossible.
There are many distinct radio bands available to users that transmit digital data, starting at 30-50 MHz and extending into the VHF range (220 MHz to 450-470 MHz, and 900 MHz). Available frequency bands with the exception of the 900 MHz band require a license from the Federal Communications Commission (FCC) for permission to operate, and such operation is covered by Part 90 of the FCC rules and regulations. The 450-470 MHz band is authorized for primary use by occasional voice service, on a shared use basis with others in a particular service area. Typical users include taxi dispatch, maintenance and repair dispatch, and other business or government services that need occasional voice service and do not need access to a nationwide telecommunications service.
Most users of available communication channels are required to share the channel with other users. However, users that transmit data such as surveyors typically set up on a work site and start transmitting data packets that are typically broadcast once per second, with a duration of approximately 0.25-0.4 seconds, until the project is complete. Thus, a particular channel is virtually occupied by the transient user until the project is complete. This can create problems for other users, particularly when a radio channel is used for which there is a local area repeater system. If the data packets are picked up by the repeater system, they are rebroadcast over a much larger area. This renders the particular channel completely useless over a large area. Even if the user's signal is not repeated, the user's strong signal may “capture” the repeater's receiver and thereby prevent voice users from using the repeater.
For the above reasons, a channel formerly used by local voice users can become unusable for the entire time period in which data is transmitted. When an established user, at his base of operations, cannot access the user's mobile fleet in a few seconds, his options are few: wait until the channel clears, or reassign each radio in the fleet to a new channel. This is inconvenient and time consuming for the established user. This also can lead to complaints by the local established users to the FCC for failure to abide by the rules of operation established by the FCC that call for sharing the channel.
The FCC requires that voice users listen before they speak to assure that the channel is available. However, in many instances users do not listen for a sufficient amount of time. This often results in voice users talking over a digital data transmitter's transmission. This can result in loss of data. If the voice usage is significant, this may force the user of the digital data transmitter to change to a less congested frequency band.
What is needed is a method and apparatus that will allow for more efficient use of available frequency bands. Also, a method and apparatus is needed that meets the above needs and that does not interfere with voice communication. In addition, a method and apparatus is needed that meets the above needs and that is inexpensive and easy to operate.